Synthesis and phase engineering of low-dimensional TMDs and related material structures

Two-dimensional (2D) transition metal dichalcogenides (TMDs), an indispensable member of the 2D family and a perfect complement to graphene, have long been at the center of research attention, attributed to their large spectrum of fascinating properties along with the various crystal structures. Recent research has demonstrated that in addition to the composition of a material, phases play a crucial role in determining its fundamental properties. Engineering 2D TMDs into designated phases is therefore of increasing importance for improving the material properties and meeting the requirements of different applications. In this chapter, we focus on the recent developments in the phase engineering of 2D TMDs. The crystal structures of 2D TMDs, including 1H, 2H, 3R, 1T, and 1T', are introduced first. Common synthesis methods in terms of top-down and bottom-up approaches are then summarized. Various strategies to engineer the phases of 2D TMD are particularly presented, which are classified into two categories: direct synthesis of TMDs with targeted phases and external factor-induced phase transformation.